1. Field of the Invention
The present invention relates to a device for decoding a still picture and, more particularly, to a decoding device capable of displaying high-resolution still picture with limited memory.
2. Description of Related Art
Recently, because the video and multimedia applications have become so popular, the video compress and de-compress techniques, such as MPEG1, MPEG2 and H.263, are in wide spread use. FIG. 8 shows the structure that implements the compress and de-compress process. First, bit-stream data is read from a storage media 88 and then sent to a variable-length decoder (VLD) 81 for decompressing the Huffman data. A run-length decoder (RLD) 82 is provided to pad zeros into the decompressed Huffman data and send it to an inverse quantizer (INVQ) 83 to reconstruct time domain data. Finally, an inverse discrete cosine transformation (IDCT) unit 84 is provided to process the data to complete the decoding process. When the process is applied to a general system, for example, VCD, SVCD, or DVD, there are many high-resolution still picture applications. The high-resolution data is decoded and stored in dynamic random access memory (DRAM) 85 to furnish displaying data on the television device 86. In the VCD application, the data size of a PAL full frame is 704×576×1.5=608,256 bytes. However, in a typically VCD application, the system usually has 4M bit DRAM, which is equal to 512 K byte and is obviously less than 608,256 bytes. Moreover, there may be other demands for memory, such as the memory for processing OSD (On Screen Display) and audio signal. Therefore, it is difficult to achieve the aforementioned functions with limited memory.
To solve the problem, a direct way is to discard part of the picture data for decreasing the required memory. However, this may significantly reduce the output resolution and thus derogate the output image quality. Therefore, there is a need to have a novel design for displaying high-resolution still picture with limited memory.